Japanese Patent Application Laid-Open No. 2010-162804 discloses an image forming apparatus in which an image is recorded by ejecting ink from nozzles while an ink jet head reciprocates in a scanning direction. In the ink jet head disclosed in Japanese Patent Application Laid-Open No. 2010-162804, nozzles for black are arranged with a density of 600 dpi while nozzles for color are arranged with a density of 300 dpi. In other words, the nozzles for black are arranged with a pitch corresponding to a half of the pitch of the nozzles for color. When an image is recorded using both black ink and color ink, a series of operations are repeatedly performed in which the ink jet head is moved in the scanning direction while ink is ejected from the nozzles for black and color, and thereafter a recording sheet is conveyed by a distance corresponding to five times the pitch of the nozzles for black.
Here, in Japanese Patent Application Laid-Open No. 2010-162804, the black nozzles are divided into two black nozzle groups arranged one after another, and ink is alternately ejected from the black nozzles belonging to one and the other of the two groups at each timing of ink ejection. Alternatively, ink is ejected only from the nozzles belonging to one group while the ink jet head is moved to one side in the scanning direction, and ink is ejected only from the nozzles belonging to the other group while the ink jet head is moved to the other side in the scanning direction. By thus performing image recording, all the black nozzles have a chance to eject ink while the ink jet head is moved once in the scanning direction, so that the black nozzles can be prevented from being dry.